For the scripture saith unto Pharaoh, Even for this same purpose have I raised thee up, that I might shew my power in thee, and that my name might be declared throughout all the earth (Rom 9:17) 

God’s had not YET destroyed Pharaoh in order to further demonstrate His power. God spared Pharaoh for a while, instead of destroying Egypt more quickly. Rom. 9:17-18 is a reference to this verse:

Exodus:9:15 For now I will stretch out my hand, that I may smite thee and thy people with pestilence; and thou shalt be cut off from the earth. 16And in very deed for this cause have I raised thee up, for to shew in thee my power, and that my name may be declared throughout all the earth.17AS YET EXALTEST THOU THYSELF AGAINST MY PEOPLE; THAT THOU WILT NOT LET THEM GO? (KJV)

Notice in this reference, that Pharaoh is suggested to have exalted himself against God’s people by refusing to let his people go. This was an idea coming from Pharaoh himself and not from God. Another translation is:

Exodus 9:15-16 For by now I could have stretched out my hand and struck you and your people with a plague that would have wiped you off the earth. But I have raised you up [or have spared you, NIV mg.] for this very purpose, that I might show you my power and that my name might be proclaimed in all the earth.  

The word hardened consists of three different Hebrew words used to describe Pharaoh’s heart condition. Kabed which has the idea of to be heavy, insensible, or dull, qasah which conveys the sense of being hard, severe, or fierce, hazaq, meaning to be or grow firm, strong. The plagues are called “judgments” (7.4), because God judged Egypt in its treatment of Israel. We can read in the Bible that people “perish; because they received not the love of the truth, that they might be saved” (2 Thess 2:10) and that would have been an option also for Pharaoh. Instead he ended up much like the rebellious people spoken about in Romans 1, who God gave up to a depraved mind because of their wickedness.

There were to be ten wonders in all, each time a sign judgment would be delivered for the purpose of freeing Israel. These become more severe as the months go by (approximately 6 months). The magicians finally acknowledged; “This is the finger of God” (8:19) so the judgements were apparently effective. Pharaoh admitted this off and on through the ordeal (9.27; 10.17), the officials did likewise (9.20; 10.17), the Israelites (14.31) and many Egyptians (12.38) went with the Israelites (and were saved during the Passover judgment/plague–12.48-49), and the Philistines in Canaan honored Israel’s God and knew all about Pharaoh’s folly (I Sam 4.8; 6.5-6).

Pharaoh hardened his own heart numerous times before God did. If Pharaoh started out to harden his heart first (even though the Bible says the opposite) wouldn’t this mean that Pharaoh’s heart was NOT hard/hardened BEFORE this occurred? This is usually not what reformed believers believe could be the case with “non-elect”, but rather that wicked people have hardened hearts all the time. When is a person’s heart in risk to be hardened?

Hebr. 3:7 Wherefore as the Holy Ghost saith, To day if ye will hear his voice, 8 HARDEN NOT YOUR HEARTS, as in the provocation, in the day of temptation in the wilderness

This means that it’s our responsibility to not harden our hearts, and we can see that we get hardened hearts when hearing the voice of God and refusing to hearken to him. This could explain why we can read that God hardened Pharaoh’s heart at the same time as we read that Pharaoh hardened his own heart. Before the first contact with Moses and his God, Pharaoh’s heart was not hard/hardened because he had never faced any options about adhering to God’s requests or not. (I’m not saying Pharaoh was necessarily “saved” during that time, because he could still have lived in sin and against his own conscience.) Some might experience hardening of their own hearts and lives if they know that God is calling them to come to him – maybe through another person who evangelizes for them – but due to fear, peer pressure, or similar, they decide to reject the calling even though they believe it’s divine. They have then hardened their hearts, or we could say it’s the evangelist who hardened their hearts since he is the one who “caused” the hardening to happen by evangelizing to them. Had he not done so, they would remain in their ignorance. So both alternatives are valid depending on how we look at it. The same evangelist might approach the same people yet again, and once again “harden” them when he reminds them of that God wants them to repent for their sins and accept him as their Savior. If they once again reject the calling, they have once again hardened their hearts (or the evangelist did). I believe street preachers constantly “harden people’s hearts” when they preach to them about repentance and that God is calling them to come to him to get life. Even though some of them realize that they do live in sin and really should turn their lives around, they still choose to reject the offer.

Pharaoh is said to have hardened his heart in the below verses

Ex 8:15 But when Pharaoh saw that there was respite, he hardened his heart, and hearkened not unto them; as the LORD had said.

Ex 8:32 And Pharaoh hardened his heart at this time also, neither would he let the people go.

Ex 9:34 And when Pharaoh saw that the rain and the hail and the thunders were ceased, he sinned yet more, and hardened his heart, he and his servants. (Here we can read that Pharao SINNED by hardening his heart, so if we want to believe God is the one hardening it, then GOD is the one who forced Pharao to sin.)

1 Sam 6:6 Wherefore then do ye harden your hearts, as the Egyptians and Pharaoh hardened their hearts? when he had wrought wonderfully among them, did they not let the people go, and they departed? (Here the pagan kings understood the root cause of Pharaoh’s problem was HIS OWN hardening.)

Verses in Exodus with no source of agent mentioned

7:13 “Pharaoh’s heart was hard (“and the heart of Pharaoh is strong, and he hath not hearkened unto them, as Jehovah hath spoken” / Young’s Literal)
7:14 “Pharaoh’s heart is unyielding
7:22 “Pharaoh’s heart was hard
8:19 “Pharaoh’s heart was hard”
9:7 “Pharaoh’s heart was unyielding”
9:35 “Pharaoh’s heart was hard”

God is said to have done the hardening in the below verses in Exodus:

4:21 “I will harden his heart” (future – a prophesy)
7:3 “I will harden Pharaoh’s heart” (future – prophesy)
9:12 “God hardened Pharaoh’s heart”
10:1 “I have hardened his heart”
10:20 “God hardened Pharaoh’s heart”
10:27 “God hardened Pharaoh’s heart”
11:10 “God hardened Pharaoh’s heart”
14:4 “I will harden Pharaoh’s heart”
14:8 “God hardened Pharaoh’s heart”
14:17 “I will harden the Egyptians’ hearts”  

This means, that the first mention of someone hardening Pharaoh’s heart is in Ex. 8:15, where Pharaoh is said to have done it. Not that it matters, considering what I’ve written above. This is what might have happened to Pharaoh:

Romans 1:21 Because that, when they knew God, they glorified him not as God, neither were thankful; but became vain in their imaginations, and their foolish heart was darkened.22 Professing themselves to be wise, they became fools,23 And changed the glory of the uncorruptible God into an image made like to corruptible man, and to birds, and fourfooted beasts, and creeping things.24 Wherefore God also gave them up to uncleanness through the lusts of their own hearts, to dishonour their own bodies between themselves:25 Who changed the truth of God into a lie, and worshipped and served the creature more than the Creator, who is blessed for ever. Amen.26 For this cause God gave them up unto vile affections: for even their women did change the natural use into that which is against nature:—28 And even as they did not like to retain God in their knowledge, God GAVE THEM OVER TO A REPROBATE MIND, to do those things which are not convenient;—31 Without understanding, covenantbreakers, without natural affection, implacable, unmerciful:32 Who knowing the judgment of God, that they which commit such things are worthy of death, not only do the same, but have pleasure in them that do them.

Examples of hardening of a heart

2 Chron 36:11 Zedekiah was one and twenty years old when he began to reign, and reigned eleven years in Jerusalem. 12 And he did that which was evil in the sight of the LORD his God, and humbled not himself before Jeremiah the prophet speaking from the mouth of the LORD.13 And he also rebelled against king Nebuchadnezzar, who had made him swear by God: but he stiffened his neck, and hardened his heart from turning unto the LORD God of Israel.

Ps 95:7For he is our God; and we are the people of his pasture, and the sheep of his hand. To day if ye will hear his voice, 8 Harden not your heart, as in the provocation, and as in the day of temptation in the wilderness:

Pro 28:13He that covereth his sins shall not prosper: but whoso confesseth and forsaketh them shall have mercy.14 Happy is the man that feareth always: but he that hardeneth his heart shall fall into mischief.

Pro_21:29 A wicked man hardeneth his face: but as for the upright, he directeth his way. 

Isaiah 63: 17 O LORD, why hast thou made us to err from thy ways, and hardened our heart from thy fear? Return for thy servants’ sake, the tribes of thine inheritance.18 The people of thy holiness have possessed it but a little while: our adversaries have trodden down thy sanctuary. (Notice that one could be aware of this condition and ask God to change it. Pharaoh could have done the same thing.)

Dan 5:18 O thou king, the most high God gave Nebuchadnezzar thy father a kingdom, and majesty, and glory, and honour: 19And for the majesty that he gave him, all people, nations, and languages, trembled and feared before him: whom he would he slew; and whom he would he kept alive; and whom he would he set up; and whom he would he put down. 20 But when his heart was lifted up, and his mind hardened in pride, he was deposed from his kingly throne, and they took his glory from him (Note the means of self-hardening was pride. In this case, God punished the ruler with deposition rather than additional and prolonging hardening)

Deut 15:7 If there be among you a poor man of one of thy brethren within any of thy gates in thy land which the LORD thy God giveth thee, thou shalt not harden thine heart, nor shut thine hand from thy poor brother:8 But thou shalt open thine hand wide unto him, and shalt surely lend him sufficient for his need, in that which he wanteth.9 Beware that there be not a thought in thy wicked heart, saying, The seventh year, the year of release, is at hand; and thine eye be evil against thy poor brother, and thou givest him nought; and he cry unto the LORD against thee, and it be sin unto thee.

Deut. 10:16 Circumcise therefore the foreskin of your heart, and be no more stiffnecked. 17For the LORD your God is God of gods, and Lord of lords, a great God, a mighty, and a terrible, which regardeth not persons, nor taketh reward

Jer. 4:4 Circumcise yourselves to the LORD, and take away the foreskins of your heart, ye men of Judah and inhabitants of Jerusalem: lest my fury come forth like fire, and burn that none can quench it, because of the evil of your doings.

Deut 30:1 And it shall come to pass, when all these things are come upon thee, the blessing and the curse, which I have set before thee, and thou shalt call them to mind among all the nations, whither the LORD thy God hath driven thee,2 And shalt return unto the LORD thy God, and shalt obey his voice according to all that I command thee this day, thou and thy children, with all thine heart, and with all thy soul; 3That then the LORD thy God will turn thy captivity, and have compassion upon thee, and will return and gather thee from all the nations, whither the LORD thy God hath scattered thee. 4If any of thine be driven out unto the outmost parts of heaven, from thence will the LORD thy God gather thee, and from thence will he fetch thee: 5And the LORD thy God will bring thee into the land which thy fathers possessed, and thou shalt possess it; and he will do thee good, and multiply thee above thy fathers. 6And the LORD thy God will circumcise thine heart, and the heart of thy seed, to love the LORD thy God with all thine heart, and with all thy soul, that thou mayest live. (Notice that God will circumcise their hearts AFTER they return to Him which is a condition.)

Ps 119: 17 Deal bountifully with thy servant, that I may live, and keep thy word. 18Open thou mine eyes, that I may behold wondrous things out of thy law (Notice that the writer can see well enough to know he needs ‘more visibility)

1 King. 8:58 That he may incline our hearts unto him, to walk in all his ways, and to keep his commandments, and his statutes, and his judgments, which he commanded our fathers.59 And let these my words, wherewith I have made supplication before the LORD, be nigh unto the LORD our God day and night, that he maintain the cause of his servant, and the cause of his people Israel at all times, as the matter shall require:60That all the people of the earth may know that the LORD is God, and that there is none else.61 Let your heart therefore be perfect with the LORD our God, to walk in his statutes, and to keep his commandments, as at this day. (Notice that one can ask God to turn our hearts)

2 Chron. 12:¹⁴ And he did evil, because he prepared not his heart to seek the Lord.

1 Chron. 29:18 O LORD God of Abraham, Isaac, and of Israel, our fathers, keep this for ever in the imagination of the thoughts of the heart of thy people, and prepare their heart unto thee: 19 And give unto Solomon my son a perfect heart, to keep thy commandments, thy testimonies, and thy statutes, and to do all these things, and to build the palace, for the which I have made provision. (Notice that these things can be prayed for)

Mark 9:²³Jesus said unto him, If thou canst believe, all things are possible to him that believeth. ²⁴And straightway the father of the child cried out, and said with tears, Lord, I believe; help thou mine unbelief. (This person expressed faith and asked to be given more faith. We know when we need “unhardening” or renewal)